Events recorder

ABSTRACT

A sequential operations events recorder is disclosed wherein alarm points or circuits are monitored for providing a printed record in alphanumeric characters the changes in state or event of each of the alarm points or circuits in timed sequence. The first of a series of events is documented in printed form by the recorder to feature a &#39;&#39;&#39;&#39;first out&#39;&#39;&#39;&#39; indication.

United States Patent Ben A. Harris lrondequoit, N.Y.

Jan. 28, 1969 Sept. 7, 1971 Rochester Instrument Systems, Inc.

{72] Inventor [21 1 Appl. No. [22] Filed [45 I Patented [7 3 Assignee[54] EVENTS RECORDER 8 Claims, 5 Drawing Figs.

[52] US. 340/415, 340/412, 340/213, 340/324 [511 m. (I osh 19/99, H04q3100 50 Field oISeareh 340/213,

INVERTER NETWORK CIRCUIT osrecron "'l cmcurr DETECTOR L. cmcurr M3355cmcun' 20 V (RESET) [56] References Cited UNITED STATES PATENTS2,963,692 12/ 1960 Barter et al. 340/251 3,029,421 4/1962 Beguin 340/4153,138,791 6/1964 Beguin 340/415 3,264,613 8/1966 Stolle 340/2233,264,626 8/1966 Mounce 340/2131 Primary Examiner-John W. CaldwellAssistant Examiner-Robert J. Mooney Attorney-Samuel R. Genca ABSTRACT: Asequential operations events recorder is disclosed wherein alarm pointsor circuits are monitored for providing a printed record in alphanumericcharacters the changes in state or event of each of the alarm points orcircuits in timed sequence. The first of a series of events isdocumented in printed form by the recorder to feature a first outindication.

SELECT GATE MEMORY CIRCUIT ABNORMAL PATENIEU SEP 1 I97! SHEET 2 BF 3 Naom M535 omoumm mum vm J zmozmd m. w CD050 mohowkmo now INVENTOR. BEN A.HARRIS Fl'go N 6d+ on 1 63+ ATTORNEY SHEET 3 [IF 3 -(HI)VOLTS +(L0)VOLTS 6 L IL -(LO)VOLTS 38 Fig. 3

PATENTED SEP 7 mm m m E V m BEN A. HARRIS BELL RET

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. to normal and a permanent record of a time sequence of the variableand its identification is recorded.

BACKGROUND OF THE INVENTION Prior art annunciators employing illuminateddisplays are well known to those skilled in the art. Such annunicatorshave been used in thepast for displaying by illuminated panels'thechange in state viz normal or abnormal of many alarm points or circuitsin a system. A change in state in one of the alarm points in the pastusually required a manual correction in the system before the systemreturned to the normal state. With the advent of automatic equipmentmany of the alarm points are self-correcting so that the illuminatedpanels in the annuneiator may only momentarily display a fault or changein state of the alarmpoint. Thus this information is very volatile sinceno record of the change of state or event is produced. Furthermore it isparticularly important to know when the first-alarm point goes abnormalin such systems. While prior art annunciators have worked satisfactorilyin the past, they have not been entirely satisfactory for automaticself-correcting systems since no permanent record of the change ofevents is recorded. Accordingly, there is a pressing need for arecording annunciator which will record the events of each alarm pointor circuit in a system in code form such as alphanumeric characters andalso give a first out" indication.

I SUMMARY OF THE INVENTION Briefly described, an events recorder inaccordance with a preferred embodiment of the invention comprises aplurality of monitor circuits each of which is coupled to acorresponding alarm point orv alarm circuit. The monitor circuits inresponse to an interrogative signal produce a first signal indicating achange in status (normal to abnormal or abnormal to normal) of the alarmcircuit and a second signal indicating the status. Scanning meanssequentially provide the interrogation signals to the monitor signalswhen enabled. A display means functional circuit also provides a seriesof sequential control signals when enabled. Switching means are coupledto the monitor circuits, scanning means and display means functionalcircuit for disabling the scanning means to continuously interrogate themonitor circuit producing the first signal and enable the display meansfunctional circuit. A signal responsive output display means or devicesuch as a signal responsive automatic typewriter, Teletypewriter or thelike is included. A circuit means-is coupled to the output displaymeans, scanning means, the plurality ofmonitor circuits and the displaymeans functional circuit. The circuit means is responsive to the controlsignals to apply signals to the output display means identifying themonitor circuit being continuously interrogated, and indicating itsstatus. A reset circuit means is coupled to the monitor circuits forremoving the first signal in the monitor circuit being interrogated todisable the display means functional circuit and enable the scanningmeans when the status indication is completed on the display means. Themonitor circuits are sequentially monitored so that the first monitorcircuit and its associated alarm circuit which changes status is soindicated on the display means.

, BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is ablock diagram of anevents recorder showing apreferredembodiment of the invention;

FIG. 2 is a schematic diagram of the input modules included in theevents recorder-of FIG. 1;-

FIG. 3 is a schematic diagram of detection circuits included in theinput module of FIG. 2;

FIG. 4 is a simplified schematic diagram of portions of inverter-networkand memory circuits included in the input module of FIG. 2; and

FIG. 5 illustrates an example of the timing sequence for transferringinformation to the output display means included in the events recorderof FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The events recorder of thepresent invention provides for a visual and permanent indication of thetype of change in status of alarm-circuits, the location oridentification thereof, and time and sequence of occurrence, in a codedor alphanumeric form, thereby providing sufficient information so thatimmediate steps can be taken to provide proper maintenance. The changeor event to occur first is recorded first, followed by subsequentlychanging alarms in a time of occurrence sequence, or interrogationsequence, depending upon the rate at which the changes occur. The eventsrecorder also includes interrogation means for providing a summary ofevents for all of the alarm points in which a change occurred.

The events recorder illustrated by the basic block diagram of FIG. 1continuously scans a large number of alarm circuits or alarm contactpoints 20a20n to detect any change in their status (on to off, open toclosed, etc.). When a change in status of an alarm point 20a-20n isdetected, the scanning stops and the identification of the alarm point20a-20n, type of change (normal to abnormal or vice versa) and the timethe change of status occurred, is then recorded by an output displaydevice 10. The output display means or device 10 can be a printer,teleprinter, automatic signal responsive typewriter and the like, thatprints a hard copy or permanent record in an alphanumeric form. Althoughthe events recorder of FIG. 1 is described as monitoring relay contacts20a-20n and recording their status on the output display device 10, itwill be apparent from this description that the present invention isequally applicable to monitor other types of alarm points, contacts,transducers and the like, to provide a display on a variety of outputdisplay devices without loss of advantage, or the necessity of materialchange or alteration beyond that obvious to one skilled in the art.

The same reference numerals have been used through the figures in thedrawings to designate the corresponding elements wherever possible so asto maintain closer correspondence between the respective figures therebyfacilitating a ready understanding of the relationship therebetween.

Referring now to FIG. 2, the events recorder includes an inputmodule 11that continuously monitors the status of the alarm circuits or fieldcontacts 20a20n, where a represents the first contact and n representsthe n" contact of a plurality of contacts 20a-20n. The. input module 11includes a plurality of monitor circuits 20-211 corresponding to thecontacts 20an, that is a separate monitor circuit 2a-2n is employed foreach of the field contacts 20a-20n. The monitor-circuits 2a-2n detect,remember and indicate any change in the status of its connected alarmcircuits or contacts 20a20n, respectively.

Each of the monitor circuits 2a-2n is identical. Each monitor circuit2a-2n includes a correspondingly lettered detector circuit (l2a-l2n), aninverter-network circuit (Ma-Mn), memory circuit (l6a-16n) and a selectgate circuit (I8a-l8n In the preferred embodiment illustrated, the alarmcircuit or contacts 20a-20n include normally open contacts indicating anormal operating condition, however normally closed contacts or othertypes of switching devices such as transducers can also be used toprovide an indicating variable, such as a presence or absence of asignal.

' It should be understood that the field contacts or contact points20a-20n are representative of normal or abnormal conditions and may forexample be included in alarm contacts or transducers that areconventionally connected to a system or apparatus to be monitored, suchas turbines, generating stations, unmanned substations, etc. The contactpoints 20a20n and associated relays (not shown) are energized ordeenergized when the monitored temperature, pressure, voltage, etc.,reach an overload or abnormal condition to produce an alarm signal.

A separate schematic diagram representative of the detector circuitsl2a-l2n is illustrated in FIG. 3. Each of the detector circuits l2a-12ncomprises a relay which includes a coil 24 and corresponding contacts 38that are activated in response to a change in status of the connectedone of the alarm contacts (a-20a). The detector relay coil 24 isconnected in series with a diode 26 and a resistor 28 between a negativelow voltage (about 24 volts) at a terminal 30 and a negative highvoltage (about 100 volts) at a terminal 32. A diode 34 is connectedacross the coil 24 to prevent high voltage spikes when the coil 24 isdeenergized. The alarm contacts 20a (in the case of detector circuit120) are connected between a positive low voltage (about 24 volts) at aterminal 36 and the junction of the diode 26 and the resistor 28. Whenthe contacts 20a are open the diode 26 is back-biased and the relay coil24 is deenergized. When the contacts 20a close, the diode 26 is forwardbiased and the relay coil 24 is energized to close its contacts 38. Therelay coil 24 remains energized as long as the connected alarm contacts20a remain closed.

When the alarm contacts 20a-20a initially close, the high voltage acrossthe contacts (about 124 volts) provides an arcing effect that cleans thecontacts and assures a low impedance connection for current flow betweenthe terminals 36 and 32 (FIG. 2). This is important since the alarmcontacts 20a-20 are often located in areas subject to adverse ambientconditions, such as high humidity and variable temperatures which mayproduce excessive corrosion. Corroded alarm contacts tend to presentpoor electrical connections that often severely limit current flow andreduce their reliability. The arcing effect of the high voltage acrossthe contacts 20a-20n eliminates or substantially minimizes thisdetrimental effect of corrosion.

The detector relay contacts 38, when closed, connect the common line 40,or ground, to an inverter circuit 42, a resistor 44 and a terminal at 50designated as NC (normally closed) and NO (normally open) (FIG. 2). Theoutput of the inverter circuit 42 is connected to NO terminal, aresistor 46 and a capacitor 48. A connection is made between the NCterminal or the NO terminal and an output terminal 50 depending upon thetype of contact point 20a employed. In the embodiment illustrated, thecontact points 20a-20n are normally open (NO) and are in the opencondition during normal operation and the connection made betweenterminal 50 and the NO terminal. If the contact points 20a were anormally closed (NC) contact point then the connection would be madebetween the NC terminal and terminal 50. Thus the connection madebetween terminal 50 and the NC terminal or the NO terminal is apermanent connection and does not change once set. The resistors 44 and46 are connected to a positive low voltage power supply (about 5 volts)at a terminal 52. The opposite end of the capacitor 48 is connected toan output terminal 54.

The memory circuit l6al6n includes a pair of NOR gate circuits 60 and 62connected to form a latch type of flip-flop circuit (60,62) (FIGS. 2-4).The particular logic circuits illustrated in FIGS. 24 employs negativelogic," that is a high level voltage represents a logic 0 whereas a lowlevel voltage represents a logic 1. It should be understood of coursethat other logic schemes may be used without departing from theinvention. The latch flip'flop circuit (60,62) employs a normallyundesirable contact resonance or bounce (characteristic to mostelectromechanical switches) to an advantage by using the resultantpulsating signals to latch" the flip-flop circuit (60,62). When thedetector relay coil 24 is energized, the contacts 38 are rapidly broughttogether. However, due to the resiliency of the contacts 38, thecontacts 38 bounce apart several times before they come to rest and aresecurely connected. It is well known to those skilled in the art thatuncom pensated contacts do bounce" and are generally cheaper thancompensated contacts such as mercury wetted contacts. Thus lessexpensive contacts may be used in the practice of the present inventioneven though they are normally undesirable because of contact bounce.

The bouncing of the contacts 38 causes a varying direct current voltageor pulsating signal on the output of the inverter circuit 42 whichcharges the capacitor 48 through a resistor 64 and the series diodes66-69 which define a reactive circuit.

When the capacitor 48 becomes sufficiently charged at output terminal 54to produce a logic 0 at the input circuit 70 of the NOR gate 60, theflip-flop circuit (60,62) is latched to produce a logic 0 at its outputterminal 61. When the relay is deenergized, a single pulse is producedappropriately polarized for latching the flip-flop circuit (60,62). Theflipflop circuit (60,62) could also be latched by applying a logic 0 toa second input circuit 72 of the NOR gate 60. The flip-flop circuit(60,62) is unlatched by applying a logic 0 to the input 74 of the NORgate 62. The flip-flop circuit (60,62) is latched whenever there hasbeen a change in the status of the connected alarm contacts 20a from anormal" open condition to a closed abnormal" or alarm" condition, andvice versa (provided the flip-flop circuit (60,62) has been previouslyunlatched").

The memory circuits 16a-l6n also include a pair of NOR gate and 82 (FIG.2) connected to enable the input circuits 72 and 74 of the NOR gates 60and 62 (flip-flop circuit) respectively. The NOR gate 80 is enabled tolatch" the flipflop circuit (60,62) when the events recorder is in asummary mode of operation that is when the summary push button circuit120 is operated. The NOR gate 82 is used to unlatch" the flip-flopcircuit (60,62) during a recording mode of operation. The operation andfunction of the NOR gates 80 and 82 will be fully explained hereinafter.

The select gate circuits l8a-l8n each include a NAND gate 86 and two NORgates 84,85 and are periodically interrogated in consecutive order by ascanner decoder circuit 88 (FIG. 1 One input circuit of each of the NANDgates 86 in the select gates l8a-l8n is connected to a separate terminal(designated XI, X2Xn) while the other input circuit is connected to acommon enable terminal 7 (FIG. 2). The terminals X1, X2-Xn and 7 areconnected to sequentially receive enable pulses from the scanner decodercircuit 88 to sequentially enable the select gate circuits l8a-l8n forinterrogation in consecutive order.

When the NAND gate 86 is enabled, a logic 0 is applied to' one inputcircuit of the NOR gates 84 and 85. The NOR gate 84 is enabled only ifit receives a logic 0 from the NOR gate 60 (the flip-flop circuit islatched") indicating a change in the status of the alarm contacts 20a.When enabled, the NOR gate 84 produces a record" signal on an outputterminal 90 through a diode 92 for initiating a recording mode ofoperation. The second input circuit of the NOR gate is connected to theterminal 50 and receives a logic 0 when the alarm-contact 20a is in theabnormal condition to develop a logic 0 at the signal terminal 94through a diode 96. Hence, if the alarm contacts 20a changed from anormal to an abnormal condition (open to closed) a record" signal (logic0) is developed on a terminal and an abnormal" signal (logic 0) isdeveloped on terminal 94. However, if the alarm contacts 20a changedfrom abnormal to normal, the record signal (logic 0) is again developedon terminal 94, and a normal signal (logic 1) is developed on theterminal 94.

A scanner generator circuit (FIG. 1), such as a 100 kilohertz relaxationoscillator, provides the count pulses for driving the scanner decodercircuit 88. The scanner counterdecoder circuit 88, in response to thecount pulses, generates gating signals that are sequentially applied tothe terminals Xl-Xn (FIG. 2) and enables or interrogates one select gatecircuit 18 after another in consecutive order. The terminal 90 isconnected to the scanner generator circuit 100 through an interlockcircuit 102 to stop the generator circuit 100 when an interrogatedselect gate circuit indicates a change in status.

plete a counting cycle every 100 input pulses.

It should be understood of course that more or less contacts i 20a-20may be used without departing from the invention. A gating circuit (notshown) is connected to the units counter so that a logic 1 is producedsequentially on l0 separate output circuits for each counting cycle.Similarly a gating circuit (not shown) is connected to the tens counterso that a logic 1 is produced sequentially on separate output circuitfor each counting cycle. The output circuit of the units and tens gatingcircuits is connected to a matrix circuit (not shown) to select adifferent one out of a hundred output for sequentially applying theinterrogation signals to the monitor circuits 2a2n in the input module11 and interrogates the monitor circuits 2a-2n in rotation. When thescanner generator 100 is stopped by the recor signal on terminal 90, theunits and tens counters hold a constant count corresponding to themonitor circuit 2a-2n indicating the change in status and keep theselect gate circuit l8a-l8n enabled until the recording is completed onthe display device 10.

The record" terminal 90 is also connected through the interlock circuit102 to enable a baud counter 104 for initiating the record cycle. A baudgenerator or oscillator circuit 114 applies ll0 hertz count pulses tothe baud counter 104 and also advance signals to a serializer circuit115. The baud counter 104, when enabled by the record signal, completesa count cycle every 1 l pulses from the baud generator 114 to apply acarry pulse (10 characters per second) to a 13 count cycle charactercounter circuit 116.

The 13 possible positions of the character counter 116 are gated to acharacter decoder circuit 118 to produce a logic 1 on one of 13 outputcircuits according to the position of the character counter circuit 116.It should be understood that more or less counts can be included in thecharacter counter circuit 116. The outputs from the character decoder118 are labeled according to the position of the counter during thestrobe interval whereby a logic 1 is produced. For example, the linelabeled 8C3 indicates that a logic 1 is applied to the line during theposition 3 of the character counter 116.

The line labeled SC8 applies a logic 1 from the character counterdecoder 118 to the terminal V (FIG. 2) at the position 8 of thecharacter counter 116. The logic 1 is inverted by an inverter circuit106 (FIG. 2) to apply a logic 0 to the NOR gate circuit 82 in each ofthe memory circuits l8a-l8n. The other input circuit of the NOR gate 82was previously enabled by a logic 0 from the NAND gate 86. The NOR gate82 now applies a logic 0 to the NOR gate 62 which unlatches the memorycircuit flip-flop (60,62) and allows the scanner counter decoder 88 toproceed after the recording has been completed. The interlock circuit102 inhibits the scanner generator 100 while the flip-flop circuit 60,62is reset by way of line SC8. That is the flip-flop circuit 60,62 isreset after the alarm point units (PAU) have been interrogated.

Once unlatched, the latch flip-flop circuit (60,62) can detect asubsequent change in the same alarm circuit or contacts a20n. With theflip-flop circuit (60,62) unlatched no record" signal is generated andtherefore only a single recording is made of each change in status ofthe alarm contacts 20a-20n. A single recording such as time, contactidentification and status provide the necessary alarm information.

It should be noted, although the flip-flop circuit (60,62) is unlatchedduring a recording cycle, a signal is still generated by the NOR gates85 at the signal terminal 94 indicating the condition of the alarmcontacts 20a-20n as the LII various monitoring circuits 2a-2n areinterrogated. If a summary of the alarm circuits or contacts 20a-20n inthe abnormal condition is desired, a logic 1 from a summary pushbuttoncircuit 120 is applied to the terminal U (FIG. 2) wherein the NAND gate108 is enabled to apply a logic 0 to an input circuit of the NOR gate inall the memory circuits 16. If the connected alarm contacts 20a20n arein an abnormal condition, the other input circuit of the NOR gate 80receives a logic 0 from the terminal 50 and therefore applies a logic 0to the NOR gate 60 to latch" the memory circuit flip-flop (60,62). Arecord" signal is therefore generated for each monitor circuit 2 a-Zn totest the alarm contacts 20a20n for an abnormal or normal condition. Thescanner decoder circuit 88 will therefore be stopped at each monitorcircuit 2a-2n to observe an abnormal condition and to make a recording,regardless of whether or not a prior recording was made. A reset signalis applied to the inverter 106 during each recording as previouslymentioned to disable the NAND gate 108 and apply a logic 0 to the NORgate 82 to unlatch the flip-flop circuit (60,62) for the particularmemory circuit l6a-l6n being recorded. As a result, only a singlerecording of each ab normal indicating monitor circuit 2a-2n is madeeach time a summary cycle is initiated.

A time generator circuit or oscillator 110, synchronized to the 60 hertzline mains, provides 60 hertz timing pulses to a digital time counter112. If for any reason the 60 hertz input is interrupted, the timegenerator circuit 110 continues to operate at approximately 60 hertz forextended periods of time resulting in only a small error. The digitaltime counter 112 includes flip-flop circuits (not shown) which countdown the pulses to second units, second tens, minute unit, minute tens,hour units and hour tens. When synchronized to the 60 cycle line mains,a counting cycle is completed every 24 hours. The digital time counter112 provides the time information at the time of printout on the outputdisplay device 10.

A decoder circuit 122 is coupled to the baud generator 114 and the baudcounter 104 to generate a strobe pulse in the order of severalmilliseconds every time the baud counter 104 reaches the count positionthree. The strobe pulse is applied to two gate circuits 124 and 126 andalso the serializer 115. The gate circuits 124 and 126 are also coupledto the C2 and C 2 outputs of the second stage of the character counter116 to apply strobe counting signals to the character decoder 118. Theoutputs from the eight counting stages of the character counter 116 arealso applied to the character decoder 118.

The signals from the gates 124 and 126 and from the character counter 116 are combined by the character decoder 118 to produce the controlsignals (SCO-SC12) for sequencing the presentation of variable and fixedinformation for loading in parallel into the serializer 115. The outputsof the gates 124 and 126 are combined with the outputs from thecharacter counter 116 so that the control signals SCl-8,10,1l and 12have durations corresponding to the duration of the strobe pulses.

The time information from the digital time counter 112 is applied to atime encoder circuit 128. The output from the interlock circuit 102 andthe output from the character counter 116 at the start of the count 8through 12 are applied to the input of a NOR gate 87 to inhibit the timechange of the digital time counter 112 whenever the baud counter 104 isenabled except during the character counts 8 through 12 (FIG. 5). Thedigital time counter 112 includes a flip-flop for storing a time changerequest from the time generator 110 until the absence of an inhibitingfunction from the NOR gate 87. The time generator 110 produces a timechange request once every second. The alarm circuit identificationinformation (scan position) from the scanner counterdecoder 88 isapplied to a scanner encoder circuit 130. The signal terminal 94 (FIG.2) is coupled to an A-N (abnormal-normal) encoder circuit 132.

A special function encoder 134 provides the signals for print controlfunctions, such as, bell, space, return, line feed, etc. The outputcircuits of the encoders 128, 130, 132 and 134 are coupled via aplurality of data lines for parallel loading the variable and fixedinformation into the serializer 115.

The encoder circuits 128, 130, 132 and 134 are connected so that theyare enabled by the output gating signals of the character counterdecoder118. The encoder circuits define the display means functional circuits.The lines to the various encoder circuits 128, 130, 132 and 134 aredesignated by sequential control signals (SCO-SCIZ) applied thereto. Forexample, the encoder 128 is enabled by the control signals SCO-corresponding to the first six counts of the character counter 116, totransmit the time data to the serializer 115. ln response to the controlsignals, information from the encoders 128, 130, 132 and 134 is appliedto the serializer 115, and the serializer is advanced by pulses from thebaud generator 114 and marches information through an amplifier 140 tothe output display device 10. The line labeled 8C3 between the characterdecoder 118 and the digital time counter 112 inhibits any time changewhen recording seconds. After an entire recording is completed, the baudcounter 104 stops the character counter 116 to O causing the characterdecoder 118 to inhibit the baud counter 104 via line 142.

FIG. 5 is an illustration of the sequence of the information and controlsignals presented to an output display device as a function of the countpositions of the character counter 116. The information is abbreviatedin accordance to numerical order (0-12) as hours tens (HT), hours units(HU), minute tens (MT), minutes units (MU), second tens (T), secondunits (SU), space (SP), alarm tens (PAT), alarm units (PAU), status (N)normal or (A) abnormal (STA), return (RET), line feed (LF) and bell.When an alarm point (contact a-20n) changes status a recording cycleinitiated as mentioned above and a 13 character message is initiated forrecording an alphanumeric printout, one line per event, as illustratedbelow in Table I.

Table 1 Reading from left to right, the first six digits are for time inhours, minutes and seconds, a space, two digits for alarm point numberand last status change. Thus the scanner decoder 88 resumes operationand both the baud counter 104 and the character counter 116 remain inthe 0 count position until another change in state occurs in any one ofthe alarm contacts 20a20n.

The NOR gate 85 in the select gate circuits l8a-18n (FIG. 2) provides anoutput signal corresponding to the last event that occurred just priorto printout which in this particular case would be an N (normal) typesignal.

The recording consumes a modest amount of paper, even when recordinglengthy sequences of changes. The alphanumeric printout is easy for anoperator to interpret. For example the top row indicates at 11 hours, 12minutes and 31 seconds, alarm contact 3 changed from normal (N) toabnormal (A). The second row indicates that at l 1 hours, 23 minutes and34 seconds, alarm 5 changed from abnormal (A) to normal (N). As anexample, it is possible that an alarm contact may change from normal toabnormal and back to normal during the recording of a prior alarm orevent. In such case, a recording will still be made despite the numberof changes in status. This is due to the fact that the flip-flop circuit(60,62) in the memory circuits (1611-1611) is latched" and remains inthis state until unlatched" by a printing in a manner as heretoforementioned. This condition can be readily interpreted by an operator byscanning the previous recordings for any prior change in the same alarmpoint. Accordingly it can be seen, as long as there has been a change instatus, there will be a recording.

The events recorder of the invention can readily monitor a large numberof alarm circuits, transducers or contacts. The alarm circuits orcontacts can either be open or closed during a normal operatingcondition. A readily readable alphanumeric printout is provided toindicate hours, minutes, seconds, point identity and point statusfollowed by an audible bell signal. The first-to-alarm circuit isrecorded first, followed by alarm points in scanning order. However, ifthe time difference between alarms is greater than required forprintout, the alarms will be recorded in a time of occurrence sequence.Only a single recording of a change of status is made, however aprintout of all abnormal points can be made by initiating the summarymode of operation.

While there has been described one specific embodiment of the inventionfor purposes of illustration, it is contemplated that numerous changesmay be made without departing from the spirit of the invention.

What is claimed is:

1. A circuit for indicating a change in the status of an alarm circuitcomprising:

a. switching means responsive to a change in the status of said alarmcircuit for providing a series of signal pulses,

b. bistable circuit means having first and second input circuits forswitching into first and second modes of operation respectively,

c.a reactive circuit coupling said switching means to said first inputcircuit for switching said bistable circuit means into said first modeof operation in response to said signal pulses for indicating a changein status of said alarm circuit, and

d. circuit means coupled to said second input circuit for switching saidbistable circuit into said second mode of operation for conditioningsaid bistable switching means to indicate a subsequent change in statusof said alarm circuit.

2. The invention defined in claim 1 wherein:

said alarm circuit has a first and a second status of operation; and

said switching means is coupled to said alarm circuit to produce saidseries of pulses each time said alarm circuit switches between saidfirst and second status of operation.

3. The invention defined in claim 1 wherein:

said switching means is an electromechanical device having at least onenormally open electrical contact which exhibits contact bounce whenclosing to provide said series of pulses.

4. The invention defined in claim 1 wherein:

said bistable circuit means requires direct current signals on saidfirst and second input circuits to switch modes of operations, and

said reactive circuit charges to a sufficient magnitude in response tosaid series of pulses to switch said bistable circuit means into saidfirst mode of operationv 5. The invention defined in claim 1 wherein:

said bistable circuit includes a pair of NOR gates coupled to fonn aflip-flop circuit.

6. The invention defined in claim 1 wherein:

said reactive circuit includes a capacitor which charges to a voltagesufficient to switch said bistable circuit into one of said first andsecond modes of operation in response to said series of pulses.

7. In an events recorder for indicating a change in state of an alarmcircuit having one state when normal and a second state when abnormal,the combination comprising:

a. a source of direct current voltage,

b. relay means including a coil connected in circuit with said alarmcircuit and normally open resonant contacts connected to said sourcerepresenting one. state of said alarm circuit when open,

0. said contacts bounce upon closure to produce a varying direct currentvoltage representing said other state of said alarm circuit,

a bistable circuit means having first and second input circuits forswitching into first and second modes of operation respectively forindicating said change in state of said alarm circuit,

. a reactive circuit means coupling said relay means to said first inputcircuit for switching said bistable circuit means into said first modeof operation in response to said varying direct current voltage, and

. circuit means coupled to said second input circuit for switching saidbistable circuit into said second mode of first and second modes ofoperation in response to said varying direct current voltage.

1. A circuit for indicating a change in the status of an alarm circuitcomprising: a. switching means responsive to a change in the status ofsaid alarm circuit for providing a series of signal pulses, b. bistablecircuit means having first and second input circuits for switching intofirst and second modes of operation respectively, c. a reactive circuitcoupling said switching means to said first input circuit for switchingsaid bistable circuit means into said first mode of operation inresponse to said signal pulses for indicating a change in status of saidalarm circuit, and d. circuit means coupled to said second input circuitfor switching said bistable circuit into said second mode of operationfor conditioning said bistable switching means to indicate a subsequentchange in status of said alarm circuit.
 2. The invention defined inclaim 1 wherein: said alarm circuit has a first and a second status ofoperation; and said switching means is coupled to said alarm circuit toproduce said series of pulses each time said alarm circuit switchesbetween said first and second status of operation.
 3. The inventiondefined in claim 1 wherein: said switching means is an electromechanicaldevice having at least one normally open electrical contact whichexhibits contact bounce when closing to provide said series of pulses.4. The invention defined in claim 1 wherein: said bistable circuit meansrequires direct current signals on said first and second input circuitsto switch modes of operations, and said reactive circuit charges to asufficient magnitude in response to said series of pulses to switch saidbistable circuit means into said first mode of operation.
 5. Theinvention defined in claim 1 wherein: said bistable circuit includes apair of NOR gates coupled to form a flip-flop circuit.
 6. The inventiondefined in claim 1 wherein: said reactive circuit includes a capacitorwhich charges to a voltage sufficient to switch said bistable circuitinto one of said first and second modes of operation in response to saidseries of pulses.
 7. In an events recorder for indicating a change instate of an alarm circuit having one state when normal and a secondstate when abnormal, the combination comprising: a. a source of directcurrent voltage, b. relay means including a coil connected in circuitwith said alarm circuit and normally open resonant contacts connected tosaid source representing one state of said alarm circuit when open, c.said contacts bounce upon closure to produce a varying direct currentvoltage representing said other state of said alarm circuit, d. abistable circuit means having first and second input circuits forswitching into first and second modes of operation respectively forindicating said change in state of said alarm circuit, e. a reactivecircuit means coupling said relay means to said first input circuit forswitching said bistable circuit means into said first mode of operationin response to said varying direct current voltage, and f. circuit meanscoupled to said second input circuit for switching said bistable circuitinto said second mode of operation for conditioning said bistableswitching means to indicate a subsequent change in the state of saidalarm switching circuit when said resonant contacts open.
 8. Theinvention defined in claim 7 wherein said reactive circuit meansincludes a capacitor which charges to a voltage sufficient to switchsaid bistable circuit means into one of said first and second modes ofoperation in response to said varying direct current voltage.